Field of the Invention
The present disclosure relates to a fixing apparatus included in an electrophotographic image forming apparatus.
Description of the Related Art
Electromagnetic induction heat generating systems are known as fixing apparatuses mounted in image forming apparatuses, such as an electrophotographic copying machine and a printer. In such fixing apparatuses, a fixing apparatus that includes a rotary member including a conducive layer, a helical coil provided inside the rotary member, and a magnetic core with ends that is provided in a helical shaped portion of the coil, in which the entire circumference of the conductive layer generates heat has been disclosed in recent years (Japanese Patent Laid-Open No. 2014-026267). The fixing apparatus distributes high-frequency current to the coil to generate a magnetic flux in a generatrix direction of the rotary member, generates heat in the conductive layer with an induced current flowing in a circumferential direction of the conductive layer. Then, a toner image that is formed on a recording material is fixed to the recording material with the heat of the rotary member.
Since the entire circumference of the conductive layer generates heat, the fixing apparatus has an advantage in that the time period needed for warm up the fixing apparatus is short.
However, in the fixing apparatus of Japanese Patent Laid-Open No 2014-026267, since the magnetic flux density decreases from the middle portion to the end portions of the magnetic core in the generatrix direction of the rotary member, the fixability at the end portions tend to decrease. Furthermore, when attempting to increase the heat generation amount at the end portions, the temperature in the sheet non-passing areas may rise adversely.